Some JS Testing...

dummy.js

const getSiblings = element => {
  let siblings = []
  let sibling = element.parentNode.firstChild

  while (sibling = sibling.nextSibling) {
    if (sibling.nodeType === 1 && sibling !== element) {
      siblings.push(sibling)
    }
  }

  return siblings
}

const removeActiveSiblingClass = (currentElement, activeClass = 'active') => {
  let activeElement = currentElement.parentElement.querySelector('.active')

  if (activeElement) {
    activeElement.classList.remove(activeClass)
  }
}

document.querySelector('#dummy').addEventListener('click', (e) => {
  e.preventDefault()

  if (e.target.tagName === 'LI') {
    removeActiveSiblingClass(e.target, 'active')
    e.target.classList.add('active')
  }
}, false)